The invention discloses a demercuration catalyst for flue gas and a preparation method and applications thereof. Bentonite is taken as the matrix of the carrier material of the demercuration catalyst.Starch is intercalated into bentonite to form a starch-bentonite composite. The active components are loaded on the surface of the starch-bentonite composite and composed of manganese oxides and carboxyl groups, which are obtained by oxidizing hydroxyl groups of the starch molecules. The demercuration catalyst has stable and high demercuration efficiency; the preparation process does not need burning, the preparation method is simple, the activity of MnOx is guaranteed, and the energy consumption is reduced at the same time.